Some caterpillars possess amazing defense mechanisms, the kind that exist to make parents and guardians forever fretful when their kids go out to play. Other caterpillars mimic bird poop. I guess the phrase “different strokes for different folks” applies to the non-folks of the animal kingdom as well.

The photo that inspired today’s post.

Caterpillars are the larval forms of both moths and butterflies, squishy little worm-like creatures that emerge from eggs. Their squishiness makes them incredibly attractive to several members of the animal kingdom including birds and squirrels that, like me around midnight, are always on the lookout for a snack that’s easy to eat.

So to become a bit more difficult to eat, several species’ caterpillars have evolved features along their bodies that discourage other animals from poking at them, usually through the always discouraging use of toxic chemicals. The larval forms of such frequent flyers as the Io Moth, the Buck Moth, and the Hag Moth all have bodies lined with stinging hairs and quills that are connected to poison sacs. These hairs can break skin, allowing the toxic chemical to seep beneath them. Humans who get stung by these caterpillars may experience symptoms ranging from minor irritation to everybody’s favorite, intestinal discomfort.

Given how most people feel about having a churning sensation in their lower abdomens, it’s understandable that a lot of people avoid touching caterpillars just to be on the safe side. The majority of caterpillars are not stinging caterpillars, though. Unlike the stinging caterpillars listed above, others have bumps on their bodies that appear harmful but really are just for show.

One such caterpillar is the Black Swallowtail. During some of its larval stages (and larval stages are called instars, in case you were wondering, since science has names for everything), the Black Swallowtail’s body is lined with orange bumps that protrude from the surface. They look dangerous, because often in nature red and orange are used as colors that warn predators that they’re hunting something that will seriously screw them up, but Black Swallowtail caterpillars are considered by some people one of the best caterpillars for budding entomologists to try to raise.

So how do Black Swallowtail larvae stay safe? Well, they do have one protrusion that actually does mess with other animals. It’s called an osmeterium, and it’s a Y-shaped horn located at the back of the caterpillar’s head that pops out when the little squirmster is frightened and gets retracted when it once again feels safe. The osmeterium shoots a musty-smelling liquid that, while not harmful to humans, is tinged with a distinct whiff of eau du displeasure, enough to suggest that backing away is a good idea.

But before the osmeterium even comes into play, the Black Swallowtail caterpillar defends itself in another way: similar to the Tiger Swallowtail caterpillar, during its earlier instars, its body bears a splotchy white marking right in the middle. Does this white mark carry the same suggestion of poison that red body markings do? Nope. Does it make the caterpillar look like an unappetizing piece of bird poop that squirrels and other animals are likely to pass over without a second thought? It sure does!